The impact velocity of the bullet was no more than 200 m/s, far lower than the speed of sound, therefore the possible effect of shock waves can be ignored.54 Since the bullet only grazed the abdomen at a moderate velocity, the effect of pressure wave can also be ignored. As we saw in §3, a very fast spinning NATO projectile, fired from an M16A2, makes a complete turn in 7 in. The yawing and tumbling angular velocity of the lead bullet is much slower than the spinning angular velocity of the NATO projectile. Hence the rotational motion of the bullet makes negligible contribution to the length and depth of the graze wound. We conclude that the abdominal wound was formed by the bullet pushing the skin tissue in its way, a familiar mechanical process. The inexplicable question is, how is it possible for a lead bullet, 1 cm long and 0.8 cm in diameter, to produce a graze wound 1-2 cm deep, just by pushing the skin tissue in contact with it?
The sheer length of the graze wound, 11 cm long, is another mind-boggling feature. When a bullet grazes the abdomen, there is a normal component of the reaction force exerted on the bullet by the skin, which tends to push the bullet away from the abdomen. The bullet yaws and tumbles, which also tends to make the bullet move away from the abdomen. There is no external force pressing the bullet toward the skin in the normal direction. In addition, the abdomen has a curved surface, making it far easier for a projectile to produce a two-hole penetration than an 11 cm long graze wound.